Another senator’s right to sit in the Australian parliament was questioned on Friday over a constitutional prohibition on dual citizens being lawmakers that has already ousted two senators in two weeks and threatens a third.

Senator Malcolm Roberts revealed on Thursday that he only received written confirmation that he was not a British citizen five months after he was elected in July last year as a representative of the anti-immigration, anti-Muslim One Nation party.

If Roberts were a dual citizen when he was elected, High Court precedent suggests he would have been ineligible to stand. He could be forced repay his salary and fined for each day he spent as a senator.

On that basis, Kim Jong-un could make us all citizens of North Korea and we’d all have to resign

Chris Pyne

A recent spate of political casualties due to the contentious section of the constitution has frightened some parties and threatened to alter the balance of the disparate senate where no group holds a majority.

Roberts was born in India in 1955 to an Australian mother and Welsh father. He moved to Australia as a child and said he never believed he was anything but Australian. Roberts also said he repeatedly asked the British government for confirmation that he was not a dual citizen before he nominated for election.

Roberts has refused to release the documents confirming he was not a British citizen, which he said he received in December. But he said he had legal advice that he would survive any court challenge to his eligibility.

“I’ve taken all steps that I reasonably believe necessary,” Roberts told Sky News.

The High Court has ruled that dual citizens can run for parliament if they have taken all reasonable steps to renounce their second nationality. This applies to cases involving countries that don’t allow their nationals to renounce their citizenship.

The focus was shone on lawmakers’ eligibility when a lawyer decided to investigate whether two New Zealand-born senators elected a year ago had renounced their New Zealand citizenship.

One of them, Greens party co-deputy leader, Scott Ludlam, had not. He resigned on July 14.

Four days later, the Greens’ other co-deputy leader, Larissa Waters, resigned after discovering she was a citizen of her birth country, Canada.

Australian-born government senator Matt Canavan resigned from Cabinet this week but has decided to fight to stay in parliament after discovering he is Italian.

Canavan said his Australian-born mother, who had Italian parents, had signed her son up to become Italian when she applied to an Italian consulate for citizenship in 2006.

Canavan said he had not been aware that an application for dual citizenship had been made on his behalf.

The High Court will rule on whether he is eligible to remain in the Senate, and perhaps clarify the rules around citizenship.

Senior government minister Chris Pyne said on Friday the idea that Canavan could be made a citizen of another country without his knowledge and without signing any application as a 25-year-old “is quite frankly entering the theatre of the absurd”.

“On that basis, (President) Kim Jong-un could make us all citizens of North Korea and we’d all have to resign,” Pyne told local television.

The Greens have called for an independent audit of all 226 federal lawmakers to ensure that they were all lawfully elected.

The uncertainty has raised questions about whether the eligibility section of the constitution penned in the 19th century is still relevant in an increasingly multicultural country. Australia has always been a migrant nation and has a higher proportion of overseas-born citizens than the United States.